Messages in this thread | | | Date | Mon, 21 Jun 2010 21:14:10 +0200 | From | Christoph Hellwig <> | Subject | Re: trying to understand READ_META, READ_SYNC, WRITE_SYNC & co |
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On Mon, Jun 21, 2010 at 08:56:55PM +0200, Jens Axboe wrote: > FWIW, Windows marks meta data writes and they go out with FUA set > on SATA disks. And SATA firmware prioritizes FUA writes, it's essentially > a priority bit as well as a platter access bit. So at least we have some > one else using a meta data boost. I agree that it would be a lot more > trivial to add the annotations if they didn't have scheduler impact > as well, but I still think it's a sane thing.
And we still disable the FUA bit in libata unless people set a non-standard module option..
> >> Reads are sync by nature in the block layer, so they don't get that > >> special annotation. > > > > Well, we do give them this special annotation in a few places, but we > > don't actually use it. > > For unplugging?
We use the explicit unplugging, yes - but READ_META also includes REQ_SYNC which is not used anywhere.
> > But that leaves the question why disabling the idling logical for > > data integrity ->writepage is fine? This gets called from ->fsync > > or O_SYNC writes and will have the same impact as O_DIRECT writes. > > We have never enabled idling for those. O_SYNC should get a nice > boost too, it just needs to be benchmarked and tested and then > there would be no reason not to add it.
We've only started using any kind of sync tag last year in ->writepage in commit a64c8610bd3b753c6aff58f51c04cdf0ae478c18 "block_write_full_page: Use synchronous writes for WBC_SYNC_ALL writebacks", switching from WRITE_SYNC to WRITE_SYNC_PLUG a bit later in commit 6e34eeddf7deec1444bbddab533f03f520d8458c "block_write_full_page: switch synchronous writes to use WRITE_SYNC_PLUG"
Before that we used plain WRITE, which had the normal idling logic.
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